Jeep Good running 304 until it gets HOT

[JimRico]

I got this 76 CJ7 a few months ago and have been chasing this problem that comes on only when it gets good and hot. Like sitting still or slow crawl. Thought it was vapor lock so I put in new mechanical fuel pump, re-routed fuel line and protected it along with putting in a fuel regulator. Still same problem. Holly carb was leaking so a friend gave me a freshly rebuilt MC2150. Put it in and with the help of his fuel mix O2 sensor been tweaking for a few weeks. IE: float level, idle mix adj and jets. Jacked the jets up to 52's (I know seems high for UT elevation) and float down a bit which got the lean condition better. Thought problem was gone but after a couple hour test it seems to be still there just not as bad. Also got a new gas tank and sending unit when I noticed rust in the in-line filter.

Has brand new radiator and thermostat and uses the engine fan.
Do I need a pusher fan also?
Do I need to look further into why I need #52's to get rid of lean condition?
Do I need to stop rolling when the afternoon sun is baking near 100???

Any ideas on what to look at next?

 

[flexyfool]

What are the symptoms?

 

[JimRico]

Sputtering and chugging but only when real hot. Got on expressway running bad and within a mile or so it went fine like a switch.

 

[flexyfool]

I have no good insight, but I'll throw out some ideas. Use a plastic spacer under the carb to keep it cool. Get the carb to suck in cooler air somehow. If OEM filter duct the airflow to the outside. If open filter, get the hot air out of the top of the engine bay with louvers. You can also cut holes along the back edge of the hood with hole saw. This actually doesn't look too bad and helps a lot to keep the engine cool. Relocate coil or ignition module to a cooler location. Re-torque intake manifold -- maybe it is slightly loose and warps when hot.

 

[gijohn40]

^^^^^^x2

 

[JimRico]

I have no good insight, but I'll throw out some ideas. Use a plastic spacer under the carb to keep it cool. Get the carb to suck in cooler air somehow. If OEM filter duct the airflow to the outside. If open filter, get the hot air out of the top of the engine bay with louvers. You can also cut holes along the back edge of the hood with hole saw. This actually doesn't look too bad and helps a lot to keep the engine cool. Relocate coil or ignition module to a cooler location. Re-torque intake manifold -- maybe it is slightly loose and warps when hot.

At this point I'll take any ideas I can get.
I already have a plastic spacer and thick gasket under carb and left the OE filter one it so maybe some ducting will work. Would love to find some louvers for the sides of the hood but so far only full hood ones.

It might come down to the holes. I just hate popping holes in a good non-rusted original hood. Are we talking a row of smaller 1/2in holes or a few 1-2inchers. What have you seen?

The ignition module is brand new and well away from any heat and the coil is on front of engine near fan so I'm doubting that.

I never really thought about the intake. Maybe I can do some type of leak check on it. Starter fluid or ???

Will see what I can do. THANKS FOR THE IDEAS FLEXY!!! I'll try some of these but may not know till I take it out for a full test run next week in Providence. Rico

 

[jackjoh]

Did you check your fuel filter and for a pinched fuel line? I know you mention both, just wanted to make sure. Is your engine overheating? I remember once having to run some Gunk through and engine to clean all the small ports in the water flow through the head and intake manifold.

 

[flexyfool]

It might come down to the holes. I just hate popping holes in a good non-rusted original hood. Are we talking a row of smaller 1/2in holes or a few 1-2inchers. What have you seen?

I have used four 1.75" DIAM holes between the hinges and between the channel support and the back edge. The air coming out was so hot that it would burn skin.

 

[JimRico]

I replaces both fuel filters(clear inline and screw in on carb) when I got rid of my rusty tank for a new one. I don't think it's overheating because the gauge goes from cold to about the middle then doesn't move when engine gets hotter. No coolant coming out overflow. It had a repaired radiator that leaked and the vehicle sat for 10+ years in a barn so plugged water jackets are possible. If I find an intake leak like Flexy mentioned I might end up taking off the intake so I can look at that point.
Worth checking. Thanks Jack

 

[BCGPER]

You're not by chance running the craptastic Motorcraft ignition that AMC was so fond of back then are you? if so, you might want to swap out the ignition module.

 

[JimRico]

You're not by chance running the craptastic Motorcraft ignition that AMC was so fond of back then are you? if so, you might want to swap out the ignition module.

It's got the prestolite with a new ignition box. Working on upgrading the distributor cap with an adaptor and a larger top. Supposed to prevent crossfire. Probably upgrade with the matching wires too. Hoping I don't have to fork out the cash for a MSD CDI box.

 

[RustEoldtrux]

I have electric fuel pumps plumbed into the fuel lines between the tanks and mechanical fuel pumps on 2 of my old trucks. When they begin to vapor lock, I just flip them on, and the vapor lock symptoms go away immediately. This is typically travelling slow on hot days. When things cool down, or travel speed increases to improve cooling, I can usually turn the electric pumps off again. This is a fairly cheap and effective way to overcome vapor lock on carbureted engines. The newer fuel formulas allow vapor lock to occur readily than the old leaded fuel formulas.

 

[jackjoh]

I have electric fuel pumps plumbed into the fuel lines between the tanks and mechanical fuel pumps on 2 of my old trucks. When they begin to vapor lock, I just flip them on, and the vapor lock symptoms go away immediately. This is typically travelling slow on hot days. When things cool down, or travel speed increases to improve cooling, I can usually turn the electric pumps off again. This is a fairly cheap and effective way to overcome vapor lock on carbureted engines. The newer fuel formulas allow vapor lock to occur readily than the old leaded fuel formulas.

Yes.

 

[JimRico]

Thanks guys.. A friend also told me to get an electric between the tank and mechanical pump so it's off to get an electric fuel pump and play with this distributor cap b4 I put a new one on. Then to get it good and hot to test it.

I read about smaller distributors "becoming electronically charged causing crossfire" Supposedly to prevent this you can drill a couple vent holes between terminals. But then you need to worry about contamination. Maybe I'll try that on this old cap before I install a new one. (From MSD website)

I appreciate the help guys.... Rico

 

[larrybenny]

I had the same problem only with the 258 6 cyl. There is an HEI (chev type distributer) made to drop in the engine (for the 6 cyl anyway) that I got at Time distributing. just hook it up to 12v ignition terminal. Then you can throw away the ignition module. Never had the problem again.

 

[larrybenny]

I also converted to the mc 2100 as well. for a carb, it worked better than anything else.

 

[gcb17]

I'll second (or 3rd) the electric fuel pump suggestion. Mine had similar issues and has had ZERO since I installed a cheapo electric fuel pump. I fully removed the manual one, and keep a spare in the back just in case. Runs great.

 

[JimRico]

I also converted to the mc 2100 as well. for a carb, it worked better than anything else.

I'll second (or 3rd) the electric fuel pump suggestion. Mine had similar issues and has had ZERO since I installed a cheapo electric fuel pump. I fully removed the manual one, and keep a spare in the back just in case. Runs great.

Yea Larry, My buddy swears by them If your gonna carb it. It runs really good once I got it jetted right.

gcb--- I did put the electric in as a backup, Manual pump is brand new. Don't notice much difference and it didn't help my problem when heated up. I think it's electrical.

I tried a bunch of stuff like a high quality rotor/cap/wires, a new ignition module, ducting fresh air intake and even a mod for the distributor cap. Nothing has helped. I took the hood off b4 I came to work but ran out of time to heat it up. If that fixesz then I'll have to punch some holes in it to vent. Maybe fab up a hood scoop type vent to cover the holes.

We'll see what hapens tomorrow.... Thanks for the ideas.

 

[JimRico]

Installed a bypass filter instead of the inline to help regulate the fuel and problem solved. Has a 3rd line to return excess gas to the tank. When installed level with the carb it helps prevent fuel from draining out when you shut down. Works great. Ran it up and down the mountains all weekend without a problem.
Thanks folks. Rico